i had some feedback from VW Driver regarding GTI International, basically you register your forum as a club, space allocation for the club is dealt with as follows; members have to book advance tickets at the discount rate and state the forum, they then allocate club display space according to the number of members booked against that club display, therefore groups are not constrained by numbers.
The reason behind this is previosuly clubs have stated 40-50 cars will turn up and space as been allocated accordingly but only 12-14 cars have turned up.
hope this helps